1. Field of the Invention
This invention relates to stable water-in-oil emulsions that are usable as bioadherent, ingestible systems. The systems are designed to coat and adhere to epithelial and mucosal membranes of the esophagus and gastrointestinal (GI) tract for extended periods of time. The purpose of the coating is to protect the membranes of the esophagus and GI tract against gastric fluid, while promoting healing caused by esophagitis, ulcers, and so forth and to release active drug over a controlled release rate.
2. Description of the Prior Art
Although a need for water-in-oil emulsions having a high water or aqueous phase content has long existed for use in pharmaceuticals, cosmetic and toiletry preparations, such as night creams or barrier creams, moisturizing creams and lotions, it has been difficult to provide such emulsion where the aqueous phase exceeds 45% to 55% on a weight to weight basis. Although many benefits are to be derived from providing a high water content in a water-in-oil emulsion system for cosmetic applications in particular, formulators have not heretofore been able to add more than about 50% water to the emulsion without seriously affecting the shelf life stability of the preparation. It is to be appreciated in this respect that because of the time delay that occurs between formulation of a product and commercial sale, it is undesirable to employ an emulsion which will break in a short period of time, particularly when exposed to temperature extremes that are encountered during transportation and warehouse storage. Although stability under normal climatic conditions is an asset, at the very minimum the emulsion system should be able to withstand temperatures on the order of 43.degree. C. (110.degree. F.) for at least six months without breaking.
Water-in-oil emulsions are used in barrier preparations or pore-occluding products to provide a thin oleaginous layer over the areas of the user's skin to which the composition is applied. Increasing the amount of hydrophilic inner phase in the emulsion decreases the oily feel of the material without deleteriously effecting the overall utility of the formulation. Such formulations have greater customer appeal because the higher hydrophilic content enhances the evaporative and thereby cooling effect of the cream or lotion upon application. Products formulated from these emulsion systems are described in U.S. Pat. No. 4,385,049 to Robert C. Cuca.
The use of water-in-oil emulsions as a liquid or semi-liquid system for oral use have not been successful. U.S. Pat. No. 2,948,686 to Gianladis describes water-in-oil emulsions but the patentee was not able to incorporate more than about 52% water in his emulsion system.
The present invention overcomes these deficiencies by preparing an orally useable and stable emulsion or suspension having at least 75% of an internal hydrophylic phase with a multifunctional hydrophobic external phase containing an oil and mixtures of emulsifiers in high concentrations. Such systems enable the inventive formulation, when taken orally to coat and protect the membranes of the esophagus and GI tract against high acidity and reflux conditions while enabling an optional active drug to be released from the formulation over controlled rates of release.